/Engine/Source/Runtime/Core/Public/Internationalization/Internationalization.h
Given some culture names, populate a list of cultures that are available to be used. If bIncludeDerivedCultures, include cultures that are derived from those we passed.
[TArray](API\Runtime\Core\Containers\TArray)< FCultureRef > GetAvailableCultures ( const [TArray](API\Runtime\Core\Containers\TArray)< [FString](API\Runtime\Core\Containers\FString) > & InCultureNames, const bool bIncludeDerivedCultures )